This invention relates to a method of drawing yarns in a draw zone which is equipped with a tempering device for influencing the temperature of the yarn, and an apparatus for drawing a yarn advancing through a draw zone with a tempering device for influencing the yarn temperature.
Such a method or such an apparatus are known, for example, from DE-OS 38 08 854, as well as from DE-PS 33 46 677, and DE-AS 22 04 535. In the known draw systems, the yarn is drawn by pulling it off the spinneret at very high withdrawal speeds and/or by the speed difference of two interposed draw rolls, and in each case it is heated in the draw zone. This invention is, however, not limited to such methods, but is suitable for all draw systems, which are equipped with tempering devices for influencing the yarn temperature.
In the art, there exists a factor of uncertainty in keeping the process parameters and the produced yarn properties constant in time, namely, in that the heat transfer between the yarn and the tempering device for influencing the yarn temperature, for example, a heated draw roll, heated tube, or cooling device (see, for example German Utility Model 9306510) does not remain constant, but changes in the course of time. Such unintended changes in the heat transfer cannot be detected, since in a continuous operation it is not possible to accurately measure the yarn temperature from the viewpoint of the measuring technology, whereas the temperature of the device for influencing the yarn temperature (hereafter described as tempering device or temperature modulating device) is controllable, though, but fails to be indicative of the actual heat exchange. Such variations in the exchange of heat, may originate, for example, from contaminations or wear or other operational, but unforeseen changes.
It is the object of this invention to describe a method and an apparatus, which allow the detect and eliminate unforeseen variations in the heat exchange between the tempering device and the yarn or their consequences.